Chapter Two - Test One Flashcards
Solar radiation accounts for more than ___ of the energy that heats the earth and its atmosphere
- This energy is not distributed evenly, however, as it varies by:
- 9%
- latitude; time of day; time of year.
- It is this uneven distribution of energy that creates most of what we consider to be weather.
Rotation:
earth rotates on its axis once per 24 hours
Revolution:
earth orbits around the sun once per 365.25 days per year
The Seasons
Regulated by the amount of solar radiation received by the surface of the Earth; which is dictated by:
1) angle at which the radiation strikes the surface:
2) length of the “day” (# of daylight hours)
radiation striking the earth perpendicularly is:
- much more intense than that striking at an angle (Fig 2.3)
- traverses through less atmosphere (Fig 2.4)
- length of days allow for more radiation to reach the earth’s surface (Table 2.2)
Equinox ~ 12 hours everywhere
Earth’s Orientation
- These changes are due to the Earth being tilted by 23.5º from the plane of its elliptical orbit around the sun (Fig 2.5)
- The Earth’s axis (center of rotation) points in the same direction into space all year long; as a result:
The NH: is tilted toward the sun in summer (northern hemisphere) is tilted away from the sun in winter
Solar Elevation Angle (Noontime)
Figure 2.6 and Box 2.2 (The Analemma) provide ways to calculate the solar elevation angle (β) at local noon for any latitude and time of year. This angle can also be calculated using the following equation:
β =90-Phi-(23.5ºxcos((360(N+10))/365))
where: Phi is the latitude
N is the Julian day of the year (N=1… 365)
Solar Radiation Equation - provides an instantaneous measure of the intensity of the solar radiation (Watts) per square meter (ignoring effects of atmosphere):
J = 1367 Watts/Meters^2 x sin β
Summer Solstice “Astronomical start of summer”
Sun is at its highest position in the sky, as a result, radiation shines down on the surface:
~June 21 : Julian Day 173
- more directly than at any other time of the year.
- Longest “day” of the year
Summer Solstice “Astronomical start of summer”
each latitude (in NH) will have:
- more than 12 hours of sunlight
- the farther north you go, the greater the # of daylight hours (Table 2.2) - from Arctic Circle (66.5o N) north, 24 hours of sunlight - The noon sun is directly overhead at 23.5ºN, the: Tropic of Cancer
Notice that the sun actually rises north of east and sets north of ____ during Summer Solstice
west
Winter Solstice “Astronomical start of winter”
Sun is at its lowest position in the sky, as a result, radiation shines down on the surface:
~ December 21 : Julian Day 356
- less directly than any other time of the year
- Shortest “day” of the year
- each latitude (in NH) will have less than 12 hours of sunlight
- the farther north you go, the
lesser the # of daylight hours - from Arctic Circle (66.5ºN)
north, 24 hours of darkness - The noon sun is directly
overhead at 23.5ºS, the: Tropic of Capricorn
Notice that the sun actually rises ____ of east and sets south of west during Winter Solstice
south
Autumnal Equinox “Astronomical start of autumn”
( ~ September 23 : Julian Day 266)
Vernal Equinox “Astronomical start of spring”
( ~ March 20 : Julian Day 80)
In an equinox, each latitude (NH and SH) will have:
Exactly 12 hours of sunlight and 12 hours night (hence the name equinox)
- The noon sun is directly overhead (90º from the horizon) at: 0.0º (Equator)
Energy:
the capacity to do work
Kinetic Energy (KE):
energy associated with an object by virtue of its motion; KE = ½ mv2
Potential Energy (PE):
energy associated with an object by virtue of its position with respect to gravity
PE = mgh
Temperature:
degree of hotness or coldness of an object
- is a form of Kinetic energy
- or a measure of the average speed of all of the atoms and molecules of that object
- As The Speed Increases, T Increases
- As the speed decreases, T decreases
Heat:
is energy in the process of being transferred between substances (or within a substance):
- because of a difference in temperature (∆T) - transfer is always hot to cold
Mechanisms of Heat Transfer
Conduction, Convection/Advection, Radiation
Conduction
Transfer of heat by molecular activity from one substance to another (or within a substance)
- transfer is always from hot to cold
- the larger the ∆T, the faster the transfer
- solids, especially metals are excellent conductors
Air is a poor conductor, as a result:
conduction of heat within the atmosphere only occurs at the earth’s surface (lowest few inches) where the ∆Ts are very large
Convection
Vertical transfer of heat by the mass movement or circulation of a fluid (water, air)
- thermals - convective circulation
Advection
Horizontal transfer of heat by the mass movement or circulation of a fluid (water, air)
- warm advection
Radiation
Transfer of heat through the propagation of electromagnetic waves (Fig 2.11), which only release heat when they strike an object
- The units of these wave lengths (λ) are called: microns or micrometers (µ)
1 µ = 1 x 10^-6
Solar Radiation
- transfer occurs at the speed of light (3x10^8 m/s)
- transfer does not need a medium (molecules), therefore it can occur in the vacuum of space
As the wavelength (λ) of the radiation decreases, the amount of energy it carries increases; Gamma least safe
uv – C:
0.20 – 0.29 µ - most harmful (absorbed by Ozone)
uv – B:
0.29 – 0.32 µ - produces sun burning, skin cancer
uv – A:
0.32 – 0.40 µ - produces sun burning
The NWS and EPA have established a:
Use sunscreen with a high SPF (Sun Protection Factor) number, which indicates:
UV Index (Box 2.3, Table 2.B) to bring attention to the dangers of over exposure to the sun; the Index ranges from: 0-2 (Minimal) to 10-15 (Very High)
Percentage of UV – B that is blocked
Laws of Radiation
1) All objects emit radiant energy over a range of λ’s
2) Hotter objects emit more radiant energy than colder objects (per area)
3) The hotter the radiating object, the shorter is the λ of maximum emission
4) Objects that are good absorbers of radiation at a particular λ are also good emitters at that same λ
Stefan - Boltzmann Law
E = σ T^4
(Hotter objects emit more radiant energy than colder objects)
E : is the energy emitted by the body Watts m^-2
σ: is the Stefan Boltzmann constant:
(5.67 x 10^-8 Watts m^-2 K^-4)
T : is the temperature of the body (K)
-Notice that since T is raised to the fourth power, even a small increase in T will result in a large increase in emitted energy.
Wien’s Displacement Law
λmax = C / T
(The hotter the radiating object, the shorter is the λ of maximum emission)
λmax : wavelength (µ) of maximum radiation emitted
T : is the temperature of the object (K)
C: is Wien’s constant 2898 µ K
Earth’s (Terrestrial) Radiation as:
Longwave Radiation
Sun’s (Solar) Radiation as:
Shortwave Radiation
Although the sun emits at a maximum rate around 0.5 µ, it also emits radiation at other wavelengths as seen in the:
Solar Electromagnetic Spectrum
Human’s eyes are sensitive to radiation at wavelengths between 0.4 and 0.7 µ, this is called the:
Visible Range (43% of total)
Below the visual range are:
Ultraviolet Wavelengths (7%)
Above the visual range are:
Infrared Wavelengths (49%)
Kirchhoff’s Law
Some objects, called Blackbodies are unique in that they are both:
- perfect emitters: emit 100% of the radiation possible (for a given T)
- perfect absorbers: absorb 100% of the radiation incident upon them across all possible λ
Both the Earth and the Sun approach being ____ in that they absorb and emit with nearly 100% efficiency
Blackbodies
The atmosphere does not act like a ____!
Rather, all of the molecules of gases (N2, O2, etc) that comprise the atmosphere each act like:
Black Body;
Selective Absorbers/Emitters, they absorbs/emit very well at some λ , but absorb/emit very poorly at other λ.
Most gases, except O3 and O2:
Do not absorb short λ emitted by the sun
- most of the absorption of short λ by O3 occurs in the stratosphere and is responsible for the warm temperatures observed there
Most gases, especially H20 and CO2:
Do absorb some of the long λ emitted by the earth
- the most notable exception being the:
“Atmospheric Window” that exists at λ between 8 and 12 µ that allows the earth to cool at night through: Radiational Cooling
Clouds are present, which act to “ ____ the Atmospheric Window”, keeping cloudy nights warmer than clear nights.
close
Because the atmosphere is largely transparent to short λ solar radiation, but more absorptive of the long λ:
The atmosphere is heated from the ground up.
This is why, on average, the temperature decreases 6.5ºC for every 1000 meter increase in hgt., which as seen earlier is the: Normal Lapse Rate
As H20, CO2 and the other Greenhouse gases absorb the longwave radiation, they gain Kinetic Energy, causing them to warm and in turn re-radiate some energy back to the earth
(Figs. 2.19. 2.20), as a result:
The earth’s lower atmosphere is 33ºC (59ºF) warmer than it would be w/o the gases that comprise it !
This phenomenon is called the “Greenhouse Effect”
Because, like the glass in a greenhouse, the gases in the atmosphere allow solar radiation to penetrate, but absorb or trap the terrestrial radiation.
The concentration of several of these Greenhouse Gases (CO2, CH4, N2O) have been:
increasing due to anthropogenic emissions, which, as we saw Chapter 1, have contributed to an increase in global temperatures.
